1. Field of Invention
This invention relates generally to supplemental oil recovery and is particularly related to compositions useful in supplemental oil recovery from subterranean geological formations. More specifically, the present invention is concerned with the aforementioned compositions which include lignosulfonates which have been reacted with halocarboxylic acids, and to a process of introducing such compositions into subterranean formations and reservoirs in order to increase petroleum recovery therefrom.
2. The Prior Art
Petroleum and natural gas are commonly recovered from subterranean geological formations or reservoirs by utilizing the pressure or energy inherent therein to force the petroleum (or natural gas) up to the earth's surface through wells bored into the formation. This method is generally referred to as a primary recovery method. It has been determined, however, that a major portion of the oil present in a formation is left unrecovered by this method.
Techniques to effect recovery of petroleum remaining in a formation when the natural forces for doing so are inadequate include water flooding through the injection wells drilled into the subterranean formation. This supplemental or secondary method also leaves significant amounts of petroleum unrecovered, however, due to the poor displacement efficiency of water and oil under the conditions prevailing in the reservoir with consequent high interfacial tension between the two fluids.
Surfactants, notably petroleum sulfonates, ethylene oxide adducts or alkyl phenols, alcohols and water soluble polyglycol ethers, and the like, have been used heretofore to reduce this interfacial tension and enhance the oil recovery possible with water-flooding techniques in a further supplemental or tertiary process.
It has also been proposed, heretofore, to introduce sacrificial agents or co-surfactants, such as lignosulfonate salts, into geological formations either as micellar dispersions including a primary surfactant and hydrocarbon, or in aqueous dispersion or solution preceding the water-flooding operation. Alcohols such as butanol, isopropanol and tertiary amyl alcohol, have been used as co-surfactants, but they are weak surfactants and relatively expensive. They serve principally as solubilizing agents for the primary surfactant and do little to reduce interfacial tension.
The sacrificial agent, whatever carrier means is employed, is characteristically injected into the subterranean reservoir through injection means in the form of an injection well penetrating the reservoir in spaced relation to a production means or well through which the crude oil or petroleum, ultimately displaced by the water-flooding fluid, is brought to the surface of the earth.
The secondary surfactant or sacrificial agent is one that will compete successfully, that is effectively or preferentially, with the primary surfactant for the active adsorption sites within the recovery zone of the formation, thus reducing the premature adsorption of the more expensive primary surfactant in the water-flooding fluid or micellar dispersion while being sufficiently inexpensive to warrant its use with no expectation of recovery.
While a variety of sacrificial agents such as the lignosulfonates or alkali metal carbonates, inorganic polyphosphates and the like have experienced an established utility heretofore, the need for further improvement is sustained by the increased variety and harshness of the environments in which primary and supplemental secondary, tertiary or ensuing step-wise oil recovery operations are undertaken. Thus, while expense and adsorptive capacity remains significant criteria, properties such as improved dispersancy, and particularly, salt tolerance and heat stability have an ever-increasing significance. Consequently, if a secondary surfactant and sacrificial agent could be developed that would incorporate the necessary properties of preferential adsorption in subterranean reservoirs while demonstrating significantly increased dispersant activity, salt tolerance and stability at the elevated temperatures frequently encountered by the increased depths at which recovery operations are now carried out without a material increase in the effective cost of the agent, a significant advance in the state of the art would be accomplished.
It is, therefore, an object of this invention to provide a novel sacrificial agent and secondary surfactant for use at a variety of stages in the petroleum recovery process that is inexpensive to produce and has a high preferential adsorptive capacity with respect to the primary surfactants employed in the petroleum recovery operation.
It is also an object of this invention to provide novel sacrificial agents characterized by increased dispersancy, salt tolerance and heat stability for use in petroleum recovery operations.
It is a further object of this invention to provide an improved method and apparatus for production of sacrificial agents and secondary surfactants for use in supplemental petroleum recovery from petroleum reservoirs.
The foregoing and other advantages of this invention will become more apparent from the ensuing detailed description.